Rosie has built a nest and now considers her toys(and possibly some of the cushions) to be her puppies.

We get a lot of questions about female dogs having their menstrual periods. Do dogs have menstrual periods? How long do they last? How often do they come?

In fact, the menstrual cycle is a primate phenomenon; dogs do not have menstrual periods. They have anestrus cycle that includes a period of false pregnancy. This false pregnancy, or pseudocyesis (pronounced “sudo-sigh-eesis”), can get out of control, lasting for weeks with the dog producing milk and sometimes mothering soft toys or pillows like “Rosie” in the above illustration. So what should one do when this happens?

Before talking about treatment, let’s explain the natural estrus cycle of the dog. The female dog comes into season approximately every 6 to 8 months, though this period becomes more erratic with age and is somewhat irregular when cycles first begin. The exception to the every 6 to 8 months rule are the Basenji and sometimes working sled dogs who cycle once a year. When female dogs get older (say, age 7 or older) they do not stop cycling; there is nothing similar to menopause.

The first phase of the cycle is called proestrus and is characterized by a swollen vulva, a bloody vaginal discharge, and attraction of male dogs. She flirts with the male but will not allow him to mount. The bloody vaginal discharge is what seems to lead to the misconception that the dog is menstruating. In fact, the blood comes directly from the walls of the vagina rather than the sloughing of the uterine lining as occurs in menstruation.

The second phase of the cycle is called estrus, which is characterized by the change in character of the vaginal discharge from bloody to straw colored. At this time the female begins to allow the male to mount. It is classically the change from proestrus to estrus that ovulation occurs and the female is most fertile.

Canine reproductive tract showing corpus luteum

After the mating and the discharge is over, the period of diestrus begins. The female is hormonally pregnant regardless of whether or not she is actually pregnant. During this time progesterone is produced by a structure in the ovary called a corpus luteum. This structure is produced by ovulation when the ova (eggs) are released. If the dog is pregnant, other hormones will eventually take over to maintain the corpus luteum for the entire 63 days of the pregnancy. If she is not pregnant, the corpus luteum must simply wear out before she goes back into the period of hormonal inactivity in which she spends the bulk of her time. The corpus luteum wears out slowly (rather than suddenly as in pregnancy and puppy birth) over 70 days or longer. Remember, during this time her body essentially thinks she is pregnant. All the hormones are present; only the puppies are missing.

CLINICAL FALSE PREGNANCY

When false pregnancy persists it can be a nuisance. The female dog can show the following signs:

Nesting

Mothering inanimate objects

Lactating (giving milk)

Abdominal distension

She can even appear to go into labor.

Some female dogs are very sensitive to the hormonal fluctuations of their cycle. Diagnosis is made by history and physical examination rather than by blood test. The key is to find symptoms of pregnancy in a female dog who is not pregnant. Symptoms generally become noticeable 6 to 12 weeks after estrus.

TREATMENT

If symptoms are mild, treatment is unnecessary as the condition resolves within 3 weeks. It may be tempting to put warm compresses on the breasts or wrap them to prevent milk leakage in the house. It is important to remember that any touching of the mammary tissue stimulates milk production, so it is important to minimize tactile stimulation. If the female is licking herself, she may need an Elizabethan collar to minimize stimulation.

If a more aggressive approach is needed, a diuretic such as furosemide can be prescribed. The idea is that mild dehydration will end the lactation. Some people may want to try water deprivation but this is potentially dangerous and should not be attempted without specific veterinary guidance.

If the above medication does not work, hormonal medications can be used. Progesterone can be used but after the course of medication is complete, the false pregnancy recurs so this is not a good choice. Estrogens are also not a good choice as they bring the dog back into estrus (vaginal discharge, attracting males etc.). A week’s course of the male hormone mibolerone has generally been successful but this medication is no longer available.

Hormones that inhibit prolactin (the hormone of milk production) are currently the best choices when medications are needed. Bromocriptine can be obtained from a compounding pharmacy and is given until lactation ceases (about a week or two). Upset stomach is not unusual with this medication. Cabergoline has fewer side effects and is given similarly but tends to be more expensive. Both these medications will cause abortion if the dog actually turns out to be pregnant so it is important to be sure.

The Witness Relaxin test can reliably detect canine pregnancy after 30 days from the breeding date.Ask your veterinarian about this blood test ifyou are not sure about whether your dog is pregnant.

SPAY DURING FALSE PREGNANCY?

It might seem like a good idea to spay the female to end the false pregnancy as spaying will remove the ovaries and the corpora lutea they carry. Unfortunately, this does not end the prolactin production from the pituitary gland so spaying may actually prolong the false pregnancy. It is best to wait until the false pregnancy is over and then spay her to prevent future episodes.